1. Field of the Invention
The present invention relates generally to virtual antenna mapping, and more specifically, to a virtual antenna mapping method and apparatus for feedback of virtual antenna mapping information in a Multiple Input Multiple Output (MIMO) system.
2. Description of the Related Art
To meet the demand for wireless data traffic having increased since deployment of 4G communication systems, efforts have been made to develop an improved 5G or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘Beyond 4G Network’ or a ‘Post LTE System’.
The 5G communication system is implemented in higher frequency (mmWave) bands, e.g., 6 OGHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, massive Multiple-Input Multiple-Output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna, and analog beam forming, large scale antenna techniques are discussed in 5G communication systems.
In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud Radio Access Networks (RANs), ultra-dense networks, Device-to-Device (D2D) communication, wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP), reception-end interference cancellation and the like.
In the 5G system, Hybrid FSK and QAM Modulation (FQAM) and Sliding Window Superposition Coding (SWSC) as an Advanced Coding Modulation (ACM), and Filter Bank Multi Carrier (FBMC), Non-Orthogonal Multiple Access (NOMA), and Sparse Code Multiple Access (SCMA) as an advanced access technology have been developed.
Recently, attention has been paid to Multiple Input Multiple Output (MIMO) technology, in order to increase the system throughput of wireless communication systems using a plurality of antennas. In an initial stage of development of the MIMO technology, interest was focused on techniques for increasing the throughput by increasing the numbers of transmit and receive antennas. However, this interest has been gradually moving towards increasing the number of antennas of a base station, which is more easily changeable in size and complexity than the number of antennas of a mobile terminal, which is constrained in size, power, and antenna extendibility, and complex operation ability. In line with this tendency, the 3rd Generation Partnership Project (3GPP) Release 10, also referred to as Long Term Evolution Advanced (LTE-A), has adopted a transmission scheme of a base station supporting up to 3 antennas. Current studies are focused on a transmission scheme supporting up to 64 antennas in downlink.
Although the number of antennas of a base station has increased to support new transmission modes, legacy transmission modes supporting more restricted numbers of antennas, which are only part, but not all, of the antennas of the base station. For example, when using a legacy transmission mode for 4 antennas and a new transmission mode for 64 antennas, it is necessary for a base station having 64 antennas to convert a signal formatted for 64 antennas to a signal formatted for 4 antennas. In order to accomplish this conversion, there is a need of a Virtual Antenna Mapping (VAM) technology for mapping a relatively large number of physical antennas to a relatively small number of logical antennas.
A virtual antenna mapping technology for mapping 8 antennas to 4 antennas in order for an LTE-A (3GPP Release 10) base station with 8 antennas to use transmission modes designed for an LTE (3GPP Release 8) base station supporting up to 4 antennas has been introduced.
FIG. 1 is a block diagram for explaining a virtual antenna mapper for transmitting the reference signal through a Transceiver Unit (TXRU) and physical antenna in MIMO system.
Referring to FIG. 1, a conventional mapping technology includes mapping up to 8 physical antennas to 4 logical antennas, and the detailed mapping algorithm is determined by the base station independently. The conventional mapping technology maps four transmission signals to 8 physical antennas, and the algorithm of mapping each signal to two antennas is determined by the base station. In the case of M=8 as shown in FIG. 1, assuming the channel between the base station with 8 antennas and the receiver is hi, i=1, . . . 8 and the channel after being converted to 4 antennas through application of VAM technology is gi, i=1, . . . 4, the transmission mode depicted in FIG. 1 can be expressed as Equation (1):
                    Vh        =                                            [                                                                    1                                                        1                                                        0                                                        0                                                        0                                                        0                                                        0                                                        0                                                                                        0                                                        0                                                        1                                                        1                                                        0                                                        0                                                        0                                                        0                                                                                        0                                                        0                                                        0                                                        0                                                        1                                                        1                                                        0                                                        0                                                                                        0                                                        0                                                        0                                                        0                                                        0                                                        0                                                        1                                                        1                                                              ]                        ⁡                          [                                                                                          h                      1                                                                                                                                  h                      2                                                                                                                                  h                      3                                                                                                                                  h                      4                                                                                                                                  h                      5                                                                                                                                  h                      6                                                                                                                                  h                      7                                                                                                                                  h                      8                                                                                  ]                                =                                    [                                                                                          g                      1                                                                                                                                  g                      2                                                                                                                                  g                      3                                                                                                                                  g                      4                                                                                  ]                        =            g                                              (        1        )            
In Equation (1), a matrix V comprised of 1's and 0's is multiplied by a channel vector h, which is the mathematical expression of the virtual antenna mapping technology for converting the legacy transmission mode using M transmit antennas and N receive antennas. When applying the virtual antenna mapping technology, although the number of antennas of the transmitter is greater than the number of antennas of the receiver, the receiver receives data under the assumption that the transmitter has 4 antenna ports.
Such a conventional technology is used effectively when mapping 4 logical antennas (e.g., transmission mode 2 of an LTE system) to 8 physical antennas (e.g., a transmission mode of an LTE-A system).
However, the conventional antenna mapping technology is restricted to the base station implementation issue in association with the detailed mapping and not discussed to the extent of the detailed technical method. This is because the number of cases of the virtual antenna mapping patterns, in the current virtual antenna mapping technology for mapping 8 antennas to 4 antennas, is not likely to contribute to additional performance enhancements.
However, since it is expected that the future wireless communication systems will be extended to scenarios in which base stations are equipped with up to 64 antennas, there is a need of a new virtual antenna mapping technology.
In addition to the transmission modes supporting up to 4 antennas, new transmission modes for supporting more antennas are to be developed for use in association with the new techniques introduced to the LTE network. Base stations that support legacy transmission modes of 4 antennas use the virtual antenna mapping technology in order to address problems resulting from a mismatch in the number of antennas of legacy transmission mode and new transmission mode.
The virtual antenna mapping technology is restricted to a base station implementation issue, but is not actually applied to systems, due to doubts about the cost-effectiveness of performance enhancement by using such technology. However, with a recent increase in the number of antennas of base stations and application of an Active Antenna System (AAS), base stations have become more diversified in order to implement the virtual antenna mapping method, resulting in expectations of performance enhancement. Therefore, there is a need of a new design for supporting modification in the virtual antenna mapping technology other than system designs limited to the base station implementation issue.